Why Does The Lower Left Side Of My Right Leg

why does the lower left side of my right leg hurt at times so much that I can't put much weight on it? Today, I was grocery shopping and ended up using the cart almost like a crutch so I didn't have to walk on the leg...then it went away, like it usually does...very sporadic. Also, I am no athlete so am not putting stress by pounding the pavement. thank you, Ann